Back
Muderongia imparilis
Muderongia imparilis Duxbury, 1980
Now Odonotochitina. Originally Muderongia, subsequently Odonotochitina?, thirdly (and now) Odonotochitina.
Holotype: Duxbury, 1980, pl.5, figs.4,5, textfig.11B
Locus typicus: Speeton, England
Stratum typicum: Barremian
Original diagnosis: Duxbury, 1980, p. 128-129
A species of Muderongia with a finely perforate periblast produced into three well-developed horns (apical, antapical and lateral) and one whidl is greatly reduced (lateral). The lateral horns are, therefore, distinctly disproportionate with the larger one extending at right angles from the body for a short distance and then recurving towards the antapex and tapering gradually to a point. The slender lateral horn is little more than a short, distally rounded lateral projection. The endoblast is spheroidal and may exhibit projections into any of the horns. The endoblast and periblast are separate except in the epicystal region. The paracingulum is reflected by a distinct double line of folding along the lateral horns (only up to the point of recurving on the longer). The archeopyle is apical.
Observed Dimensions: Holotype (complete)--278 x 70 Ám. Complete specimens 278 (251) 223 x 70 (70) 70 Ám. Operculum Detached--159 (149)105 x 111 (106) 73 Ám.
Affinities:
Duxbury, 1980, p. 129: This species is reminiscent in several respects of Muderongia staurota Sarjeant, 1966 but differs in being generally more elongate and in the character of the lateral horns. M. staurota may, however, have lateral horns of different lengths. M. imparilis is also reminiscent of species of Odontochitina Deflandre, 1935 emend. Davey, 1970, especially O. operculata (Wetzel, 1933) Deflandre & Cookson, 1955. It differs, however, in possessing a second lateral horn, greatly reduced through this is. It is possible, therefore, that M. imparilis may represent an intermediate stage in the evolution of the genus Odontochitina from Muderongia. Wall & Evitt (1975, p. 32) have expressed their concept of Muderongia as a ceratioid dinoflagellate cyst having two lateral attenuations, each having a distal, postcingular horn. They state, "The two lateral horns in Muderongia vary considerably in length from species to species (e.g. Iong in M. tetracantha (Gocht) Alberti, 1961; short in M. simplex (Alberti, 1961)". In the present author"s view, the distinguishing feature of Muderongia is the presence of the two lateral attenuations, whether or not two distal, postcingular horns may be present. Davey (1979, pl. 2, figs. 4, 5) illustrates Muderongia sp. A from the Upper Kimmeridge Clay. His species certainly belongs in the genus Muderongia, since it is obviously an end member of the Muderongia simplex group. Neither of Davey"s illustrated specimens displays any trace of distal, postcingular horns. Similarly, one lateral projection of M. imparilis bears no distal, postcingular horn but, in the present author"s concept of the genus, must be included in Muderongia.
Now Odonotochitina. Originally Muderongia, subsequently Odonotochitina?, thirdly (and now) Odonotochitina.
Holotype: Duxbury, 1980, pl.5, figs.4,5, textfig.11B
Locus typicus: Speeton, England
Stratum typicum: Barremian
Original diagnosis: Duxbury, 1980, p. 128-129
A species of Muderongia with a finely perforate periblast produced into three well-developed horns (apical, antapical and lateral) and one whidl is greatly reduced (lateral). The lateral horns are, therefore, distinctly disproportionate with the larger one extending at right angles from the body for a short distance and then recurving towards the antapex and tapering gradually to a point. The slender lateral horn is little more than a short, distally rounded lateral projection. The endoblast is spheroidal and may exhibit projections into any of the horns. The endoblast and periblast are separate except in the epicystal region. The paracingulum is reflected by a distinct double line of folding along the lateral horns (only up to the point of recurving on the longer). The archeopyle is apical.
Observed Dimensions: Holotype (complete)--278 x 70 Ám. Complete specimens 278 (251) 223 x 70 (70) 70 Ám. Operculum Detached--159 (149)105 x 111 (106) 73 Ám.
Affinities:
Duxbury, 1980, p. 129: This species is reminiscent in several respects of Muderongia staurota Sarjeant, 1966 but differs in being generally more elongate and in the character of the lateral horns. M. staurota may, however, have lateral horns of different lengths. M. imparilis is also reminiscent of species of Odontochitina Deflandre, 1935 emend. Davey, 1970, especially O. operculata (Wetzel, 1933) Deflandre & Cookson, 1955. It differs, however, in possessing a second lateral horn, greatly reduced through this is. It is possible, therefore, that M. imparilis may represent an intermediate stage in the evolution of the genus Odontochitina from Muderongia. Wall & Evitt (1975, p. 32) have expressed their concept of Muderongia as a ceratioid dinoflagellate cyst having two lateral attenuations, each having a distal, postcingular horn. They state, "The two lateral horns in Muderongia vary considerably in length from species to species (e.g. Iong in M. tetracantha (Gocht) Alberti, 1961; short in M. simplex (Alberti, 1961)". In the present author"s view, the distinguishing feature of Muderongia is the presence of the two lateral attenuations, whether or not two distal, postcingular horns may be present. Davey (1979, pl. 2, figs. 4, 5) illustrates Muderongia sp. A from the Upper Kimmeridge Clay. His species certainly belongs in the genus Muderongia, since it is obviously an end member of the Muderongia simplex group. Neither of Davey"s illustrated specimens displays any trace of distal, postcingular horns. Similarly, one lateral projection of M. imparilis bears no distal, postcingular horn but, in the present author"s concept of the genus, must be included in Muderongia.